1. Field of the Invention
The present invention relates to a PTC thermistor device with a PTC thermistor unit housed in a case. More specifically, the present invention relates to a PTC thermistor device which is utilized in a degaussing circuit of a cathode ray tube (CRT).
2. Description of Prior Art
In a CRT circuit of a television receiver or the like, as shown in FIG. 1, by turning on a switch 1, degaussing current is caused to flow to a degaussing coil 3 via a PTC (Positive Temperature Coefficient) thermistor 2. When the degaussing is terminated, the current flowing in the degaussing coil 3 is reduced by increasing a resistance value of the PTC thermistor 2. To this end, a PTC thermistor 4 for heating is thermally coupled to the PTC thermistor 2. More specifically, at a time just after the turn on of the switch 1, the resistance value of the PTC thermistor 2 is small since its temperature is low, and therefore, a relatively large degaussing current flows in the degaussing coil 3. However, when the PTC thermistor 2 is heated by the PTC thermistor 4, since the resistance value of the PTC thermistor 2 increases, the current flowing the degaussing coil 3 is reduced.
As shown in FIG. 2, units of such two PTC thermistors 2 and 4 are respectively fixed on both main surfaces of a single holding plate 5 so as to be thermally coupled to each other. Then, in order to prevent the heat from being dispersed, the units of the PTC thermistors 2 and 4 and the holding plate 5 are accommodated or housed in a case 6. Terminals 7-9 connected to electrodes of the units of the PTC thermistors 2 and 4 are withdrawn to the outside the case 6. Thus, the PTC thermistor device is constructed.
On the other hand, in the above described CRT circuit, when the degaussing operation is terminated, in order to minimize the consumption of the electric power, it is necessary to make the current flowing the degaussing coil 3 as small as possible. Therefore, in the PTC thermistor device utilized in the CRT circuit, it is necessary to heighten a thermal equilibrium temperature of the units of the PTC thermistors 2 and 4 as much as possible by strengthening the thermal coupling between the units of the PTC thermistors 2 and 4. If and when the holding plate is made of a metallic material, the heat generated by the PTC thermistor 4 is easily dispersed through the holding plate 5 and the terminal 7. Therefore, in practice, it was impossible to heighten the thermal equilibrium temperature of the units of the PTC thermistors 2. Furthermore, in the case where a coefficient of thermal conductivity of such a metallic material is high, since the heat generated by the PTC thermistor 4 is transferred to a printed circuit board (not shown) through the terminal 7, occur such as solder on the printed circuit board being melted, and the other electronics components being thermally destroyed.